Speedo calibration

[01NavyBlueSLPSS]

While on the highway today I checked to see how off my speedo is. ( I got a big ticket for doing 48 in a 35 last week) I know my speedo is off but didn't know how much. I plugged in the predator, plugged in stock tire sizes and actual tire sizes, which are the same btw. So I calculated my speedo is off by two tenths of a mile. I did three highway runs. Reset the trip at mile points, and got 0.8 every time. All I know about the car is the previous owner had 4.11's and switched back to stock 3.42 for some reason. Is it normal for the speedo to be off by 2 tenths/5mph? Or is it possible that the gearing in the back isn't 3.42 maybe? Could someone point me to a possible gear ratio to cause the speedo to be off? Thank you

[01NavyBlueSLPSS]

Oh and btw, sorry for being such a newb I'm just used to old school shit lol

[thearborbarber]

Sounds like you have a taller rear than you are programed for. Prob a 3.23 or 2.73 if its factory gears.

[01NavyBlueSLPSS]

Popped the diff cover today. The gears are stock 3 42. Now I'm really puzzled

[35th-ANV-SS]

You could have just turned the wheel 1 revolution and counted how many turns the drive shaft made to get your gear ratio.

You probably have the speedo calibrated to a different gear still.

[01NavyBlueSLPSS]

I needed to pop the cover anyways. And according to the predator its programmed for 3 42

[35th-ANV-SS]

Do you have the stock OEM gauges?

[01NavyBlueSLPSS]

Yes they are stock. I'm thinking I need to have gm calibrate it

[35th-ANV-SS]

You could use an online calculator as another check to ensure your RPM's are matching your speed for the gear ratio you have.

I'm assuming you counted the teeth on the ring/pinion to determine your ratio?

[SteveC]

Here is a good one:

http://www.f-body.org/gears/

[01NavyBlueSLPSS]

You could use an online calculator as another check to ensure your RPM's are matching your speed for the gear ratio you have.

I'm assuming you counted the teeth on the ring/pinion to determine your ratio?

Yes I counted them. 41 drive, 12 pinion.

[2001NBMZ28]

What version predator is it? V1.00, V1.01, V1.02 and V1.03 had issues with the gear changes. There was a chart published to change the gears by tire sizes - I had to use it for my 2.73 to 3.42 swap. If you have one of those versions I have the info.

[01NavyBlueSLPSS]

What version predator is it? V1.00, V1.01, V1.02 and V1.03 had issues with the gear changes. There was a chart published to change the gears by tire sizes - I had to use it for my 2.73 to 3.42 swap. If you have one of those versions I have the info.

Mines a v1.03

[2001NBMZ28]

Did you get the predator with the car? If so maybe he used the chart to change it before. Unfortunately the runninwiththedevel faq link doesn't work anymore - but basically said "Current versions (v1.00 through v1.03) the axle ratio settings will not adjust the parameters...speedometer calibration. Temporary fix: main screen, select tune it, modify parameters, choose factory tire size and actual tire size...." For 3.42 to 4.10 factory tire size enter 275/40-17, actual tire size 235/40-14. Don't know if it'll work reversing the sizes back? Might want to visit the diablosport forums or contact them before trying. At least you know what the possible problem is and have some history. Hope this helps...

[01NavyBlueSLPSS]

Well i tried what you suggested and that threw my speedo off waaaay worse. Thanks for your input tho I appreciate it. I'll use your other suggestion and go over to the predator forums lol